brickcraft/Assets/Scripts/UI/InventorySlot.cs

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace Brickcraft.UI
{
    public class InventorySlot : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
    {
        public Text quantity;
        [HideInInspector]
        public Transform originalParent;

        private Vector3 initialPos;

        public void OnBeginDrag(PointerEventData eventData) {
        
             if (originalParent == null) {
                originalParent = transform.parent;
            }

            //GamePanel.isMovingAPanel = true;
		    //isDragging = true;
		    initialPos = transform.position;
            transform.SetParent(Menu.Instance.transform);
            GetComponent<RectTransform> ().SetAsLastSibling ();
        }

        public void OnDrag(PointerEventData eventData) {
            transform.position = eventData.position;
        }

        public void OnEndDrag(PointerEventData eventData) {
            List<RaycastResult> raycastResults = new List<RaycastResult>();
            EventSystem.current.RaycastAll(eventData, raycastResults);

            // try to find an slot
            foreach (RaycastResult raycast in raycastResults) {
                if (raycast.gameObject == gameObject) { // ignore self detection
                    continue;
                }
                InventorySlot slot = raycast.gameObject.GetComponent<InventorySlot>();

                if (slot == null) {
                    continue;
                }
                Player.Instance.switchInventorySlots(int.Parse(originalParent.name), int.Parse(raycast.gameObject.transform.parent.name));
            }
            transform.position = initialPos;
            transform.SetParent(originalParent);
        }

        public void setVisible (bool show) {
            RawImage rawImage = GetComponent<RawImage>();
            Color currColor = rawImage.color;
            currColor.a = show ? 1f : 0f;
            rawImage.color = currColor;
        
            quantity.gameObject.SetActive(show);
        }
    }
}